This invention relates generally to gas generation and, more particularly, to the indirect ignition of igniter materials such as used in inflator devices used for providing or supplying inflation gas to inflatable passive restraint systems for use in vehicles for restraining the movement of an occupant in the event of a vehicular collision.
It is well known to protect a vehicle occupant by means of safety restraint systems which self-actuate from an undeployed to a deployed state without the need for intervention by the operator, i.e., xe2x80x9cpassive restraint systems.xe2x80x9d Such systems commonly contain or include an inflatable vehicle occupant restraint or element, such as in the form of a cushion or bag, commonly referred to as an xe2x80x9cairbag cushion.xe2x80x9d In practice, such airbag cushions are typically designed to inflate or expand with gas when the vehicle encounters a sudden deceleration, such as in the event of a collision. Such airbag cushions may desirably deploy into one or more locations within the vehicle between the occupant and certain parts of the vehicle interior, such as the doors, steering wheel, instrument panel or the like, to prevent or avoid the occupant from forcibly striking such parts of the vehicle interior.
Various types or forms of such passive restraint assemblies have been developed or tailored to provide desired vehicle occupant protection such as based on either or both the position or placement of the occupant within the vehicle and the direction or nature of the vehicle collision, for example. In particular, driver side and passenger side inflatable restraint installations have found wide usage for providing protection to drivers and front seat passengers, respectively, in the event of head-on types of vehicular collisions. Driver side and passenger side inflatable restraint installations do not, however, generally provide as great as may be desired protection against vehicular impacts inflicted or imposed from directions other than head-on, i.e., xe2x80x9cside impacts.xe2x80x9d In view thereof, substantial efforts have been directed to developing inflatable restraint installations having particular effectiveness in the event of a side impact.
Upon deployment, the time period during which an airbag cushion remains pressurized is commonly referred to as xe2x80x9cstand-up time.xe2x80x9d In practice, driver side and passenger side airbag cushions are typically desirably designed to begin deflating almost instantaneously upon deployment such as to avoid presenting an undesirably hard or ungiving surface to an oppositely situated vehicle occupant. However, airbag cushions which provide substantially longer stand-up times may be required or desired in the event of certain accidents or collisions in order to provide a suitable desired level of occupant protection. For example, one particularly troublesome form of side impact is commonly referred to as a xe2x80x9croll-over.xe2x80x9d In a roll-over incident, a vehicle may undergo a partial or complete roll-over or may undergo multiple roll-overs. As will be appreciated by those skilled in the art, roll-over accidents can be particularly demanding on inflatable restraint systems. In particular, an airbag cushion designed to provide occupant protection in the event of a vehicle roll-over may be required or desired to remain pressurized for an extended or prolonged period of time, as compared to usual or typical driver side and passenger side airbag installations. For example, a roll-over protection side impact airbag cushion desirably remains pressurized or provides a stand-up time as long as about 5 seconds and, in some applications, a stand-up time of nearly 7 seconds.
One particularly effective form of side impact inflatable restraint is the subject of Hxc3x85land et al., U.S. Pat. No. 5,788,270, issued Aug. 4, 1998, the disclosure of which patent is hereby incorporated by reference herein in its entirety and made a part hereof. Inflatable elements, such as disclosed in Hxc3x85land et al., U.S. Pat. No. 5,788,270, may desirably include an inflatable portion formed from two layers of fabric with the front layer and the back layer of the fabric woven together at selected points. In particular embodiments, such selected points are arranged in vertically extending columns and serve to divide the inflatable part into a plurality of vertical parallel chambers. The spaces between the selected points permit internal venting between adjacent chambers of the inflatable element. Particular such inflatable devices/elements, such as utilized in applications to provide protection over an extended area and having a generally planar form, are frequently referred to as xe2x80x9cinflatable curtains.xe2x80x9d
Many types of inflator devices have been disclosed in the art for use in the inflating of one or more inflatable restraint system airbag cushions. Known types of inflator devices include inflators known as xe2x80x9cblow downxe2x80x9d inflators and xe2x80x9creverse flowxe2x80x9d inflators. In a blow down inflation system, a pyrotechnic or other selected material is commonly burned to create a build-up of pressure within a compressed gas storage chamber such as to result in the rupture or release of inflation gas therefrom when the internal pressure reaches a predetermined level or range. Thus, in blow down inflator devices, the opening or rupture of a seal, burst disk or the like within the inflator typically results or produces a flow of heated or elevated temperature inflation gas from the device and into an associated airbag cushion. While blow down inflation systems can desirably be of relatively lower cost and complexity, such systems can result in the delivery of inflation gas to an associated airbag cushion at a higher temperature, pressure and/or mass flow rate than may otherwise be desired.
In xe2x80x9creverse flowxe2x80x9d inflator devices, the actuating initiator and the openings wherethough the inflation gas exits from the inflator device are typically at or along the same end or side of the inflator device. Thus, in typical reverse flow inflators, the initial inflation gas exiting from the inflator device and into an associated airbag cushion is relatively cool and is later followed by heated or elevated temperature inflation gas. Consequently, reverse flow inflators which initially provide or supply a relatively cool inflation gas, followed by heated or elevated temperature inflation gas to an associated airbag cushion, can typically more easily provide or result in the more gradual deployment of the associated airbag cushion, as may be desired in particular deployment applications.
In inflatable passive restraint system design, the space requirement (commonly referred to as the xe2x80x9cenvelopexe2x80x9d) for the airbag inflator is commonly very important. The need for airbag inflators with smaller envelopes can be particularly crucial for applications involving inflation of restraint elements such as inflatable curtains. In particular, inflatable curtain cushions tend to have rather large inflation volumes while market needs, dictated at least in part by available packaging volumes, call for inflators characterized by relatively small volumes. For example, some common inflatable curtain airbag cushions have inflation volumes of up to 40 liters while an inflator envelope of no larger than about 30 mm in diameter and 400 mm in length is permitted.
One approach to satisfying the need and demand for smaller sized inflator devices capable of providing relatively large volumes of inflation gas is via the use of liquified gases such as disclosed in commonly assigned Rink, U.S. Pat. No. 5,669,629, issued Sep. 23, 1997; Rink et al., U.S. Pat. No. 5,884,938, issued Mar. 23, 1999; and Rink et al., U.S. Pat. No. 5,941,562, issued Aug. 24, 1999, for example and the disclosures of which patents are hereby incorporated by reference herein in their entirety and made a part hereof. In such an approach, the increased density of liquified gases (as compared to similar gaseous phase systems) permits the storage of a much greater mass of material in an identical volume.
The heating and/or dissociation of such stored liquids can, however, be problematic. For example, it has been found generally difficult to design reverse flow inflators such that heating and/or dissociation occurs to the desired or required extent as the diameter of the inflator gets smaller and smaller. In particular, it is generally difficult and costly to design hardware and components that are capable of producing and effectively distributing heat through such stored volumes of liquid. For example, for those inflator devices which rely on dissociation of a stored fluid such as nitrous oxide, as the length to diameter ratio (L/D ratio) for the inflator fluid storage chamber increases, it is frequently increasingly difficult to obtain heat penetration into the stored nitrous oxide fluid to the extent desired to more fully or completely realize dissociation of the nitrous oxide. Further, blow down inflators are generally less practical in such applications due to extremely high operating pressures and rise rates.
Thus, there is a need and a demand for alternative airbag inflator device ignition schemes and, in particular, there is a need and a demand for an apparatus for inflating an inflatable device as well as a method for supplying a quantity of inflation gas to an inflatable device which provides or results in improved heat transmission to stored gas source material(s) without necessitating undesirably costly design modifications or component inclusions.
A general object of the invention is to provide an improved apparatus for inflating an inflatable device as well as an improved method for supplying a quantity of inflation gas to an inflatable device.
A more specific objective of the invention is to overcome one or more of the problems described above.
The general object of the invention can be attained, at least in part, through an apparatus for inflating an inflatable device which includes a fluid storage chamber, a chamber opener and a first indirect ignition charge. In accordance with one embodiment of the invention, the fluid storage chamber has contents which, in a static state, include a supply of at least one gas source material and which at least one gas source material has a fluid form. The chamber opener is effective, upon actuation, to open the fluid storage chamber and release therefrom a quantity of inflation gas derived from at least a portion of the at least one gas source material. The first indirect ignition charge includes at least one first ignition material physically remote from the chamber opener and in indirect ignition contact therewith. As described in greater detail below relative to such an apparatus, actuation of the chamber opener results in subsequent indirect ignition of at least a portion of the first indirect ignition charge to produce a quantity of heat and with at least a portion of the quantity of heat being transmitted to the contents of the fluid storage chamber.
The prior art generally fails to provide inflator devices and methods for supplying inflation gas to an inflatable device in a manner which effectively and efficiently transmits heat to stored gas source material(s) without necessitating undesirably costly design modifications or component inclusions.
The invention further comprehends a method of supplying a quantity of inflation gas to an inflatable device. In accordance with one preferred embodiment of the invention, an apparatus which includes a fluid storage chamber, a chamber opener, and at least one indirect ignition charge, the fluid storage chamber having contents, in a static state, including a supply of at least one gas source material, the at least one gas source material having a fluid form, is employed. Further, such method involves actuating the chamber opener and indirectly igniting at least a portion of the at least one indirect ignition charge to produce heat to heat at least a portion of the supply of the at least one gas source material.
As used herein, references to xe2x80x9ccombustion,xe2x80x9d xe2x80x9ccombustion reactionsxe2x80x9d and the like are to be understood to generally refer to the exothermic reaction of a fuel with an oxidant.
As used herein, references to xe2x80x9cdissociation,xe2x80x9d xe2x80x9cdissociation reactionsxe2x80x9d and the like are to be understood to refer to the dissociation, splitting, decomposition or fragmentation of a single molecular species into two or more entities.
xe2x80x9cThermal dissociationxe2x80x9d is a dissociation controlled primarily by temperature. It will be appreciated that while pressure may, in a complex manner, also influence a thermal dissociation such as perhaps by changing the threshold temperature required for the dissociation reaction to initiate or, for example, at a higher operating pressure change the energy which may be required for the dissociation reaction to be completed, such dissociation reactions remain primarily temperature controlled.
An xe2x80x9cexothermic thermal dissociationxe2x80x9d is a thermal dissociation which liberates heat.
xe2x80x9cEquivalence ratioxe2x80x9d (xcfx86) is an expression commonly used in reference to combustion and combustion-related processes. Equivalence ratio is defined as the ratio of the actual fuel to oxidant ratio (F/O)A divided by the stoichiometric fuel to oxidant ratio (F/O)S:
xcfx86=(F/O)A/(F/O)Sxe2x80x83xe2x80x83(1) 
(A stoichiometric reaction is a unique reaction defined as one in which all the reactants are consumed and converted to products in their most stable form. For example, in the combustion of a hydrocarbon fuel with oxygen, a stoichiometric reaction is one in which the reactants are entirely consumed and converted to products entirely constituting carbon dioxide (CO2) and water vapor (H2O). Conversely, a reaction involving identical reactants is not stoichiometric if any carbon monoxide (CO) is present in the products because CO may react with O2 to form CO2, which is considered a more stable product than CO.)
For given temperature and pressure conditions, fuel and oxidant mixtures are flammable over only a specific range of equivalence ratios. Mixtures with an equivalence ratio of less than 0.25 are herein considered nonflammable, with the associated reaction being a decomposition reaction or, more specifically, a dissociative reaction, as opposed to a combustion reaction.
References to the detection or sensing of xe2x80x9coccupant presencexe2x80x9d are to be understood to refer to and include detection and/or sensing of size, weight, and/or position of an occupant under consideration.
References to inflator or inflation gas xe2x80x9coutputxe2x80x9d are to be understood to refer to inflator performance output parameters such as the quantity, supply, and rate of supply of inflation gas. With xe2x80x9cadaptive output inflators,xe2x80x9d the inflator output is generally dependent on selected operating conditions such as ambient temperature, occupant presence, seat belt usage and rate of deceleration of the motor vehicle, for example.
A xe2x80x9cpyrotechnicxe2x80x9d material, in its simplest form, consists of an oxidizing agent and a fuel that produce an exothermic, self-sustaining reaction when heated to the ignition temperature thereof.
As used herein, the term xe2x80x9cindirect ignitionxe2x80x9d, as used in reference to the ignition of a pyrotechnic or the like material, can be generally thought of as an ignition ultimately resulting from transfer of, at least part of, the energy of a shock or pressure wave into the material. It is thought that during such transfer of energy to the material, small locations of intense heating, sometimes referred to as xe2x80x9chot spotsxe2x80x9d occur, causing or resulting in the ignition. Thus, as used herein, indirect ignition, also sometimes referred to as xe2x80x9csympathetic ignitionxe2x80x9d neither requires nor relies on particle impingement to effect the ignition of a spaced apart or otherwise isolated charge of ignition material.
Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawings.